One field of application for such an arresting device is the piece of seating furniture cited as an example. It is used there, for example, for bringing the seating height into a suitable position for the respective user of this piece of seating furniture, which is retained until the next adjustment. Pieces of seating furniture, for example office chairs, are possibly also equipped with further arresting devices of this type, especially in deluxe models, for example an adjusting device for the inclination of the arms and/or the inclination of the seat surface.
Such arresting devices furthermore are also employed in automobile manufacturing, for example to maintain hatches in the open position. Other fields of application are door openers, washing machines and the like.
Up to now, such arresting devices were known in connection with so-called gas pressure springs. In this case the cylinder is filled with a gas, which can flow from the chamber in front of the piston into a chamber behind the piston and vice versa, via a valve which can be actuated from the outside. In most cases a small amount of a fluid, for example oil, is also contained in these arresting devices.
The particular disadvantage of these known arresting devices lies in their problematic capability for recycling, which is mainly a result of the liquid filling. Aside from this, they are comparatively expensive and not without danger because of the valve arrangement. An abrupt displacement into one of the two end positions has sometimes occurred when the valve malfunctioned, which at least greatly scares the user and can possibly injure him. Furthermore, unavoidable gas losses bring constant doubts whether elements which are stored or have been installed are still capable of functioning. Repairs are impossible with gas springs.
A device for adjusting the stroke of elements, in particular of office swivel chairs, is known from German Published application OS 33 46 225, wherein two hollow cylinders can be inserted into each other in the manner of a telescope. A threaded rod, which is supported on the outer cylinder, is seated axially displaceable in the inner cylinder and a rotatably seated threaded sleeve connected with the inner cylinder is in engagement therewith. The two cylinders are pushed apart by a helical compression spring attached to the interior as soon as a brake arranged above the threaded sleeve is released.
The brake comprises a conically embodied brake drum and a brake spring, which force-lockingly maintains the brake drum in a correspondingly embodied section of the inner cylinder. The brake drum can be axially displaced by an actuating element which can be operated from the outside and can thus release the threaded sleeve. If now no further axial forces are introduced into the device, the helical compression spring can push the threaded sleeve upward along the threaded flank and rotate it in the process, since the thread is an easily moving trapezoidal thread.
In order to move the threaded sleeve, i.e. the seat surface of the chair, downward, it is necessary to overcome the spring force. This is customarily achieved by sitting in the chair.
Such devices are often employed in connection with heavy office chairs, tail gates of automobiles and the like, where only a limited amount of space is available. Thus the designer of such devices is faced with the difficulty of providing sufficient space for a helical compression spring of sufficient size which, on the one hand, is capable of actually pushing up the load when the brake is released and, on the other hand, can be housed in the available space.
Further than that, the device in accordance with German published application OS 33 46 225 consists of a large number of interlaced individual parts, which make its production and assembly difficult and expensive. It is not possible to absorb large longitudinal forces, since otherwise the brake cone angle becomes too shallow and can only be released with difficulty or not at all.
German published application 36 00 399 Al discloses a spring element of the type mentioned above. This spring element has the disadvantage that the braking effect is generated by the contact of the braking elements on the interior circumference of the cylinder. A deformation of the cylinder is not unlikely with strong braking forces.